Danish investigators are reporting that long-term cell phone use does not appear to boost the risk of central nervous system (CNS) tumors.
Patrizia Frei, PhD, with the Institute of Cancer Epidemiology in Copenhagen, and colleagues conducted a nationwide study of cell phone subscribers in Denmark and found no indication of an increased risk of CNS tumors in 358,403 subscribers over the 18-year follow-up period. Nor was there a higher risk of glioma in the temporal lobes among long-term cell phone users, which the investigators said “would be the most plausible tumor location if mobile phone use was a risk.” The temporal lobe is the region of the brain with the highest absorption of energy emitted from cell phones.
The investigators’ study is the largest to date to examine a possible link between cell phone use and CNS tumors.
The number of cell phone users continues to increase, with more than 5 billion subscriptions worldwide in 2010. But the popularity of cell phones has spawned fears about potential health risks. CNS tumors are the primary concern given that the brain is the area with the largest exposure to the radiofrequency electromagnetic fields emitted by a cell phone held next to the ear.
Results from epidemiologic studies on the association between cell phone use and the risk of CNS tumors have been inconclusive, especially with respect to long-term use.
Also, most investigations have been retrospective case-control studies with self-reported data on cell phone use and are prone to bias.
The present study adds 5 years of follow-up to an earlier analysis of Danish cell phone users. Overall, 10,729 CNS tumors were diagnosed in the study period from 1990 through 2007. The group of individuals who had the longest cell phone use (ie, ≥13 yrs) had essentially the same cancer rates as those of individuals who were not cell phone subscribers.
Frei and colleagues said that their study is notable in that it used objective registry-based data on both exposure and cancer outcome, which “virtually eliminates” participation and recall bias; both of those were a problem with prior studies.
The potential misclassification of exposure may be a study drawback. “Subscription holders who are not using their phone will erroneously be classified as exposed, and people without a subscription but still using a mobile phone will erroneously be classified as unexposed,” they wrote.
Also, the dose-response analyses are based on the number of years since the first subscription, and the researchers did not have any information on how often subscribers actually used their cell phones. As a result, they were unable to determine the risk in individuals who used cell phones the most. They said that additional large studies are needed that minimize the possibility of misclassification of exposure and selection bias.
Frei P, Poulsen AH, Johansen C, Olsen JH, Steding-Jessen M, Schüz J. Use of mobile phones and risk of brain tumours: update of Danish cohort study. BMJ. 2011;343:d6387. doi: 10.1136/bmj.d6387.